Image-guided radiotherapy for rectal cancer: a systematic review

Area of Science:

• Oncology
• Radiation Oncology
• Medical Imaging

Background:

• Rectal cancer radiotherapy is evolving towards more conformal techniques.
• Rectum and mesorectum are mobile structures, impacting treatment accuracy.
• Previous reviews focused on rectal motion in other cancers, with significant variations observed.

Purpose of the Study:

• To systematically review the literature on rectal and mesorectal motion in primary rectal cancer radiotherapy.
• To evaluate the impact of organ motion on treatment delivery and target volume margins.
• To assess the role of image-guided radiotherapy (IGRT) techniques.

Main Methods:

• Systematic literature review using Medline and Embase databases.
• Keywords included 'rectal, radiotherapy, IGRT, image guided, organ motion, internal margin, target shape/volume'.
• Analysis of nine studies examining inter- and intrafractional motion using various imaging modalities.

Main Results:

• Significant upper mesorectum movement was identified, strongly related to rectal filling.
• Gender and body mass index can influence motion.
• Current margin recommendations may be inadequate for deformable rectal structures, with suggested margins of 1-3.5cm.

Conclusions:

• Image-guided radiotherapy (IGRT) techniques are crucial for improving treatment delivery in rectal cancer.
• Re-imaging and re-planning during treatment may be necessary.
• Individualized anisotropic margins and further research on optimal imaging modalities are required.